1. Technical Field
The present invention relates in general to an improved write mask and wafer process and, in particular, to an improved system and method for a charge-balanced, continuous-write mask and wafer process.
2. Description of the Related Art
Glass masks are used in magneto resistive (MR) thin film head wafer processes. Electron beam (E-beam) or laser photo-resist imaging tools are used in the production of such glass masks. Specific mask layers typically have critical overlay and image size tolerances. The critical masks used for the MR stripe layer have an additional requirement known as colinearity error, which is defined as the y-axis deviation of the back edge of a row of MR stripes from a straight line. The colinearity quality is important because it directly relates to a key magnetic performance parameter known as MR stripe height.
Historically, glass masks made by E-beam and laser mask tools had such high quality that they were an insignificant contributor to the overall control of stripe height. However, as aerial densities in disk drives increase, the need for narrower track widths and shorter stripe heights requiring tighter controls have made mask colinearity a significant detractor in achieving satisfactory stripe height requirements.
The problems associated with improving colinearity include a number of errors associated with the control of image size, image placement, and image edge fidelity, namely:                1. Positional error of the stage mechanics relative to a Cartesian grid contributes to image placement error;        2. Glass expansion during the time that it takes to write a row of stripe images contributes to image placement error;        3. Variation in the electron charging of the photo-resist can unevenly deflect the E-beam during the writing of critical edges, thereby contributing to image placement error;        4. Fracturing design data to cause critical images to be split in two and written at different times causes steps along the critical edge;        5. Image error by stray E-beams during the writing of adjacent non-critical images or structures can affect the exposure of critical images resulting in a variation in optimum development time from image to image, thereby increasing colinearity error; and        6. Where it would be desirable to write at very small spot sizes for highest resolution and accuracy, it is not practical to do so because of long write time.        
All of these problems contribute to error in image placement, image size, or image edge fidelity, which in turn increases colinearity error. The following disclosure of the present invention describes an improved E-mask making method and wafer process whereby errors generated by these problems are minimized. While laser equipment is a more state of art tool than E-beam tools, E-beam generated masks that use the present invention outperform such laser equipment. However, laser-generated masks may show superior colinearity results if continuous write methods were employed.